Image pickup apparatus

ABSTRACT

At least one exemplary embodiment is directed to an image pickup apparatus that has an external sensor for detecting brightness separately from an image sensor for obtaining an image pickup signal and controls the insertion and removal of a filter into and from an image pickup optical system in accordance with the brightness of the subject, using brightness information obtained from the external sensor and the image pickup signal.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 11/404,614 filed Apr. 13, 2006, which claims priority fromJapanese Patent Application No. 2005-129328 filed Apr. 27, 2005, theentire contents of each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical apparatus and an imagepickup apparatus, and more particularly, though not exclusively, to animage pickup apparatus capable of image pickup in at least twowavelength bands.

2. Description of the Related Art

A color image includes color information in addition to information ofshape and brightness and is therefore useful in distinguishing aphotographed object in a color image compared to a monochrome image.Therefore, normally, security cameras photograph color images. However,image sensors, such as a CCD, widely used in security cameras aresensitive to not only light in the visible wavelength range (betweenapproximately 400 nm and 700 nm) but also light in the near-infraredwavelength range (more than approximately 700 nm). Therefore, if a colorimage is photographed using the information of all ranges to which theCCD is sensitive, the colors of the photographed color image is out ofbalance. Thus, the colors of the subject cannot be accuratelyreproduced. To solve this problem, when a color image is photographed, anear infrared light cut filter (hereinafter referred to as “IR cutfilter”) for cutting near infrared light is disposed in the optical pathof the photographing light.

However, in the case of photographing a very dark subject, for example,at night outdoor or in a room with no illumination, the amount ofincident light is insufficient. Therefore, the amplification factor ofthe image signal output from the image sensor is increased. However,large amplification of the color image signal deteriorates thesignal-to-noise (S/N) ratio of the color signal and results in a noisyimage. Thus, the outline or the shape of the subject becomes unclear. Inaddition, since color information decreases at low illuminance, thevalue of the color image decreases.

Therefore, in the case of photographing at low illuminance, conventionalsystems typically abandon obtaining color information deteriorating theS/N ratio, and image processing is performed on the basis of amonochrome image comprising luminance signals only. That is to say, theIR cut filter is removed from the optical path, and instead a dummyglass for correcting the optical path length is inserted. Since nearinfrared light can be added to the luminance information, it is possibleto photograph the subject more clearly and brightly even at lowilluminance. Such a photographing mode is called “night mode” and isdiscussed in Japanese Patent Laid-Open No. 2001-45512.

Japanese Patent Laid-Open No. 2001-45512 also discusses a techniquecalled “automatic night mode” of automatically switching between thecolor and monochrome photographing modes. In addition, Japanese PatentLaid-Open No. 2000-224469 discusses a technique of automaticallyswitching to the night mode when the illuminance of the subjectdecreases using an illuminance sensor for detecting the visible lightilluminance of the subject provided separately from the image pickupoptical system.

However, the above conventional image pickup apparatus, which can havethe automatic night mode, can fail to perform appropriate automaticnight mode operation. The first cause thereof is misdetection of theilluminance. The reason of the misdetection is, for example, that theilluminance detection range (angle of view) is larger than the imagingrange (angle of view) of the image pickup optical system, or that theilluminance detection range does not exist within the imaging range ofthe image pickup optical system. No appropriate relationship between theilluminance detection range of the illuminance detection device and theimaging range of the image pickup optical system has been discussed.

The second cause is that the relationship between the imaging range(angle of view) changing with zoom operation and the timing when the IRcut filter is inserted or removed is inappropriate. Therefore, in thecase where the imaging range and the illuminance detection range of theilluminance detection device change relative to each other, theapparatuses can fail to perform appropriate automatic night modeoperation.

SUMMARY OF THE INVENTION

At least one exemplary embodiment is directed to an image pickupapparatus (e.g., a camera), that has a wavelength band selection devicecapable of being inserted into and removed from the optical path of theimage pickup optical system and that is capable of image pickup in atleast two wavelength bands, for example, visible light and infraredlight.

At least one exemplary embodiment is directed to an image pickupapparatus that has a simple configuration and is capable of appropriateautomatic switching of the automatic night mode operation.

At least one exemplary embodiment is directed to an optical apparatuswhich includes a wavelength band selection device, an inserting andremoving device, and a brightness detection device. The wavelength bandselection device transmits or removes infrared light. The inserting andremoving device inserts and removes the wavelength band selection deviceinto and from the optical path of the image pickup optical system. Thebrightness detection device is provided separately from the image pickupdevice. The brightness detection range of the brightness detectiondevice can be within the imaging range of the image pickup opticalsystem and is equivalent to or smaller than the imaging range. Theinserting and removing device is controlled on the basis of thebrightness information of the brightness detection device and thebrightness information of an area in the imaging range corresponding tothe brightness detection range.

When using the brightness detection device that is disposed at adifferent position from the image pickup optical system and has a fixeddetection range, the apparatus of at least one exemplary embodiment cancorrectly and surely switch between inserting and removing thewavelength band selection device even if the imaging range (angle ofview) of the image pickup optical system changes significantly.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the configuration of the image pickupapparatus according to the first to fourth exemplary embodiments of thepresent invention.

FIG. 2 is a block diagram showing the circuit configuration of the imagepickup apparatus according to the first and second exemplary embodimentsof the present invention.

FIG. 3 illustrates the relationship between the imaging range and theilluminance detection range of the visible light sensor in the imagepickup apparatus according to the first exemplary embodiment of thepresent invention.

FIG. 4 is a flowchart showing the operation of the image pickupapparatus according to the first exemplary embodiment of the presentinvention.

FIG. 5 illustrates the relationship between the imaging range and theilluminance detection range of the visible light sensor in the imagepickup apparatus according to the second exemplary embodiment of thepresent invention.

FIG. 6 is a flowchart showing the operation of the image pickupapparatus according to the second exemplary embodiment of the presentinvention.

FIG. 7 is a block diagram showing the circuit configuration of the imagepickup apparatus according to the third exemplary embodiment of thepresent invention.

FIG. 8 is a flowchart showing the operation of the image pickupapparatus according to the third exemplary embodiment of the presentinvention.

FIG. 9 illustrates the variation characteristic in F-number of an imagepickup lens, which can have a zoom mechanism with the diaphragmmechanism open in the image pickup apparatus according to the third andfourth exemplary embodiments of the present invention.

FIG. 10 is a flowchart showing the operation of the image pickupapparatus according to the fourth exemplary embodiment of the presentinvention.

DESCRIPTION OF THE EMBODIMENTS

The following description of at least one exemplary embodiment is merelyillustrative in nature and is in no way intended to limit the invention,its application, or uses.

Processes, techniques, apparatus, and materials as known by one ofordinary skill in the relevant art may not be discussed in detail butare intended to be part of the enabling description where appropriate,for example the fabrication of the lens elements and circuits (e.g.,zoom motor control circuit) and their materials.

In all of the examples illustrated and discussed herein any specificvalues, should be interpreted to be illustrative only and non limiting.Thus, other examples of the exemplary embodiments could have differentvalues.

Notice that similar reference numerals and letters refer to similaritems in the following figures, and thus once an item is defined in onefigure, it may not be discussed for following figures.

Exemplary embodiments will now be described with reference to thedrawings.

FIRST EXEMPLARY EMBODIMENT

FIG. 1 schematically illustrates the configuration of an image pickupapparatus according to a first exemplary embodiment of the presentinvention. In the figure, reference numeral 1 denotes an image pickuplens (image pickup optical system), and reference numeral 2 denotes theoptical axis of the image pickup lens 1. Reference numeral denotes afilter switching mechanism, which switches between an infrared cutfilter (wavelength band selection device) 4 and a transparent plate(optical path length correction device) 5 using a motor 6. Referencenumeral 7 denotes an image sensor (e.g., CCD, CMOS). Reference numeral 8denotes a visible light sensor that detects the illuminance in animaging range. The spectral sensitivity characteristic of the visiblelight sensor 8 is equivalent to the spectral sensitivity characteristicof the image sensor (e.g., CCD) 7 combined with the infrared cut filter4. Reference numeral 9 denotes the optical axis of the visible lightsensor 8. Reference numeral 10 denotes a control circuit that controlsthe image pickup apparatus. Power can be input from the outside and avideo signal can be output to the outside. Reference numeral 15 denotesa zoom motor. The zoom motor 15 moves at least part of the image pickuplens 1 along the direction of the optical axis 2, thereby changing thefocal length from wide angle to telephoto.

FIG. 2 is a block diagram showing the circuit configuration of the imagepickup apparatus shown in FIG. 1. As illustrated in FIG. 2, the controlcircuit 10 of FIG. 1 includes a camera control circuit 21, an imagesensor control circuit 22, a visible light sensor control circuit 23, avideo signal processing circuit 24, an IR cut filter control circuit 25,a photometric circuit 26, a video signal output circuit 27, and a zoommotor control circuit 28. In FIGS. 1 and 2, the incident light thatcontributes to the image pickup is incident on the image pickup lens 1,passes through the infrared cut filter 4 or the transparent plate 5, andis then incident on the image sensor 7. The light incident on the imagesensor 7 undergoes signal processing in the video signal processingcircuit 24, and a color signal or a monochrome signal is output as avideo signal from the video signal output circuit 27.

FIG. 3 illustrates the relationship between the imaging range of theimage pickup apparatus shown in FIG. 1 and the illuminance detectionrange of the visible light sensor 8. Next, the illuminance detectionrange of the visible light sensor 8 will be described with reference toFIG. 3. In FIG. 3, reference numeral 31 denotes the imaging range(photographing angle of view) of the image pickup apparatus, andreference numeral 32 denotes the illuminance detection range(illuminance detection angle of view) of the visible light sensor 8. Asillustrated in FIG. 3, the illuminance detection range 32 is within theimaging range 31. The illuminance detection range 32 is set so as to bealso within the angle of view at the wide angle end and the telephotoend of the variable power optical system of the image pickup apparatus.That is to say, the illuminance detection range 32 can be smaller thanthe imaging range 31 when the variable power optical system is at thetelephoto end as well as when the variable power optical system is atthe wide angle end. The sensitivity of the visible light sensor 8 ishighest in the direction of the optical axis 9.

In order to set the illuminance detection range 32 within the imagingrange 31, the optical axis 9 is disposed parallel to and in the vicinityof the optical axis 2 of the image pickup lens 1.

In the above-described configuration, in the color photographing mode,the infrared cut filter 4 is inserted between the image pickup lens 1and the image sensor 7, and a color signal is output as a video signalfrom the control circuit 10 to the outside. In the monochromephotographing mode, instead of the infrared cut filter 4, thetransparent plate 5 is inserted between the image pickup lens 1 and theimage sensor 7, and a monochrome signal is output as a video signal fromthe control circuit 10 to the outside.

FIG. 4 is a flowchart illustrating the operation of the image pickupapparatus shown in FIG. 1. Next, the operation of the control circuit 10that switches between the color photographing mode and the monochromephotographing mode will be described with reference to the flowchart ofFIG. 4. First, in step S101, the camera control circuit 21 determineswhether or not the present photographing mode is the night mode. If thepresent photographing mode is the night mode, in step S102, a luminancevalue (e.g., brightness) Y1 output from the visible light sensor 8 iscalculated. Next, in step S103, a luminance value (e.g., brightness) Y2of an area on the image sensor 7 equivalent to the detection range ofthe visible light sensor 8, that is to say, an area equivalent to theilluminance detection range 32 in FIG. 3 is calculated. Next, in stepS104, the difference Ydiff between the luminance value Y1 of the visiblelight sensor 8 calculated in step S102 and the luminance value Y2 of theimage sensor 7 calculated in step S103 is calculated. The calculateddifference Ydiff is a luminance component that comes from a lightcomponent cut by the infrared cut filter 4, that is to say, a lightcomponent of a wavelength longer than that of visible light. Thedifference Ydiff is zero in a light source environment that contains noinfrared component, and increases with the increasing amount of theinfrared component.

In step S105, on the basis of the luminance value Ydiff of the infraredcomponent obtained in step S104, a threshold Yth for determiningswitching of the photographing mode from the night mode to the colormode is calculated. The luminance value Yall of the entire imaging range31 on the image sensor 7 is compared with the threshold Yth. Forexample, in the case where the light source contains no infraredcomponent, when a threshold for switching from the night mode to thecolor mode is Yth1, and a rate of threshold increase according to theinfrared component Ydiff is coefficient a, the threshold Yth can beobtained from the following equation (1):

Yth=Yth1+(α* Ydiff)   (1)

As is clear from equation (1), the switching threshold Yth increaseswith the increasing amount of the infrared component of a light sourceirradiating the subject. If a light source contains a large infraredcomponent, the photographing mode is not switched from the night mode tothe color mode until the luminance value Yall of the image sensor risesto a high luminance according to the amount of the infrared component.

For example, in the case where the luminance value Yall of the imagesensor 7 exceeds the switching threshold Yth1 in a light sourceenvironment that contains a large infrared component and small visiblelight component, if the infrared cut filter 4 is simply inserted, theluminance value Yall of the image sensor 7 falls suddenly. Thus, theluminance value Yall falls below the threshold, and the photographingmode is returned to the monochrome mode. Such operations are repeated,and hunting between the modes occurs. At least one exemplary embodimentcan reduce such a phenomenon. In addition, it is clear that fitness canbe further improved by taking into account the rate of the illuminancedetection range to the imaging range in the above equation.

In step S106, the luminance value Yall of the entire imaging range 31 onthe image sensor 7 is compared with the threshold Yth obtained in stepS105. If the luminance value Yall exceeds the threshold Yth, it isdetermined in step S107 whether or not the luminance value (e.g.,brightness) of the subject stably exceeds the threshold Yth for apredetermined time Twait. If the luminance value (e.g., brightness) ofthe subject is stable, in step S108, the photographing mode is switchedfrom the night mode to the color mode. In this way, it can bedistinguished whether or not a luminance increase is temporary, andhunting can be prevented from occurring or reduced. If the luminancevalue Yall is less than or equal to the threshold Yth in step S106, theelapsed time T used in step S107 is cleared in step S109.

If the present photographing mode is not the night mode in step S101,the process proceeds to step S110. The luminance value Yall of theentire imaging range 31 on the image sensor 7 is compared with apredetermined switching threshold Yth2. If the luminance value Yall isbelow the threshold Yth2, it is determined in step S111 whether or notthe luminance value (e.g., brightness) of the subject is stably belowthe threshold Yth2 for a predetermined time Twait. If the luminancevalue (e.g., brightness) of the subject is stable, in step S112, thephotographing mode is switched from the color mode to the night mode. Inthis way, it can be distinguished whether or not a luminance decrease istemporary, and hunting can be prevented from occurring or reduced. Ifthe luminance value Yall is greater than or equal to the threshold Yth2in step S110, the elapsed time T used in step S111 is cleared in stepS113.

As described above, in the present exemplary embodiment, determinationis performed on the basis of the luminance value output from the visiblelight sensor 8 and the luminance value of an area equivalent to thedetection range 32 of the visible light sensor 8 selected from theentire range of the image sensor 7. In this way, the amount of infraredcomponent contained in the luminance information obtained from thereflection off the subject can be known. That is to say, switchingbetween the color photographing mode and the monochrome photographingmode can be appropriately performed.

SECOND EXEMPLARY EMBODIMENT

A second exemplary embodiment will be described with reference to FIGS.1, 2, 5 and 6. The hardware configuration of this exemplary embodimentis the same as that of the first exemplary embodiment (FIGS. 1 and 2).However, the software operating the camera control circuit 21 of thecontrol circuit 10 of this exemplary embodiment is different from thatof the first exemplary embodiment. FIG. 5 illustrates the relationshipbetween the imaging range of the image pickup apparatus shown in FIG. 1and the illuminance detection range of the visible light sensor 8 inthis exemplary embodiment. FIG. 6 is a flowchart showing the operationof this exemplary embodiment.

First, the illuminance detection range of the visible light sensor 8will be described with reference to FIG. 5. In the figure, referencenumeral 51 denotes the imaging range of the image pickup apparatus, andreference numeral 52 denotes the illuminance detection range of thevisible light sensor 8. As shown, the position and the area of theilluminance detection range 52 are substantially equivalent to those ofthe imaging range 51. The sensitivity of the visible light sensor 8 ishighest in the direction of the optical axis 9. In order to set theilluminance detection range 52 within the imaging range 51, the opticalaxis 9 is disposed parallel to and in the vicinity of the optical axis 2of the image pickup lens 1. The visible light sensor 8 is located, forexample, inside the lens barrel of the image pickup lens 1, and at aposition such that the visible light sensor 8 is out of the angle ofview of the image sensor 7 even when the image pickup lens 1 is set tothe wide angle end.

In the above-described configuration, in the color photographing mode,the infrared cut filter 4 is inserted between the image pickup lens 1and the image sensor 7, and a color signal is output as a video signalfrom the control circuit 10 to the outside. In the monochromephotographing mode, the transparent plate 5 is inserted between theimage pickup lens 1 and the image sensor 7, and a monochrome signal isoutput as a video signal from the control circuit 10 to the outside.

Next, the operation of the control circuit 10 that switches between thecolor photographing mode and the monochrome photographing mode, in thecase where the position and the area of the illuminance detection rangeare substantially equivalent to those of the imaging range, will bedescribed with reference to the flowchart of FIG. 6. First, in stepS301, the camera control circuit 21 determines whether or not thepresent photographing mode is the night mode. If the presentphotographing mode is the night mode, first, in step S302, the presentzoom position of the lens is referred to, and the imaging range 51 ofthe lens is calculated from the zoom position information. Next, in stepS303, it is determined whether or not the present imaging range 51 ofthe lens calculated in step S302 and the illuminance detection range 52of the visible light sensor 8 are both within a predetermined range. Ifthe imaging range 51 is substantially the same as the illuminancedetection range 52 of the visible light sensor 8, in step S304, aluminance value Y1 output from the visible light sensor 8 is calculated.In step S305, the luminance value Y1 output from the visible lightsensor 8 is compared with a predetermined switching threshold Yth1. Ifthe luminance value Y1 exceeds the threshold Yth1, it is determined instep S306 whether or not the luminance value (e.g., brightness) of thesubject stably exceeds the threshold Yth1 for a predetermined timeTwait. If the luminance value (e.g., brightness) of the subject isstable, in step S307, the photographing mode is switched from the nightmode to the color mode. In this way, it can be distinguished whether ornot a luminance increase is temporary, and hunting can be prevented fromoccurring or reduced.

If the luminance value Y1 is determined as less than or equal to theswitching threshold Yth1 in step S305, the elapsed time T used in stepS306 is cleared in step S308. If the present photographing mode is notthe night mode in step S301, determination for switching from the colormode to the night mode is performed in steps S309 to S312, as in stepsS110 to S113 of the first exemplary embodiment.

If, in step S303, at least one of the present imaging range 51 of thelens calculated in step S302 and the illuminance detection range 52 ofthe visible light sensor 8 is not within the predetermined range, theinformation from the image sensor 7 is used in addition to theinformation from the visible light sensor 8. For example, in the casewhere at least one of the present imaging range 51 of the lens and thedetection range 52 of the visible light sensor 8 is not within thepredetermined range, and the illuminance detection range 52 of thevisible light sensor 8 is within and smaller than the present imagingrange 51, the photographing mode is determined, as in the firstexemplary embodiment, on the basis of the luminance value of an area onthe image sensor 7 equivalent to the detection range 52 of the visiblelight sensor 8, and the luminance (e.g., brightness) information of thevisible light sensor 8.

As described above, the imaging range 51 of the lens is compared withthe illuminance detection range 52 of the visible light sensor 8, and ifthe imaging range 51 is substantially the same as the brightnessdetection range 52 of the visible light sensor 8, determination isperformed on the basis of the luminance information output from thevisible light sensor 8. In this way, switching between the colorphotographing mode and the monochrome photographing mode can beappropriately performed.

THIRD EXEMPLARY EMBODIMENT

A third exemplary embodiment will be described with reference to FIGS.1, 3, 7, 8, and 9. The configuration of the optical system of thisexemplary embodiment is the same as that of the first exemplaryembodiment (FIG. 1). As for the control circuit 10 of this exemplaryembodiment (FIG. 7), a zoom position correction data storage device 29is added to the control device 10 of the first exemplary embodiment(FIG. 2). The software operating the camera control circuit 21 of thecontrol circuit 10 of this exemplary embodiment (FIG. 8) is alsodifferent from that of the first exemplary embodiment. FIG. 7 is a blockdiagram showing the circuit configuration of the image pickup apparatusshown in FIG. 1. FIG. 8 is a flowchart showing the operation of thisexemplary embodiment. FIG. 9 illustrates the variation characteristic inF-number of an image pickup lens, which can have a zoom mechanism withthe diaphragm mechanism open.

As for FIG. 1 schematically illustrating the configuration of the imagepickup apparatus and FIG. 3 illustrating the relationship between theimaging range and the illuminance detection range of the visible lightsensor, their descriptions will be omitted because they have alreadybeen described in the first exemplary embodiment. First, the controlcircuit 10 in FIG. 7 will be described. The control circuit 10 includesa camera control circuit 21, an image sensor control circuit 22, avisible light sensor control circuit 23, a video signal processingcircuit 24, an IR cut filter control circuit 25, a photometric circuit26, a video signal output circuit 27, a zoom motor control circuit 28,and a zoom position correction data storage device 29. The incidentlight that contributes to the image pickup is incident on the imagepickup lens 1 in FIG. 1, passes through the infrared cut filter 4 or thetransparent plate 5, and is then incident on the image sensor 7. Thelight incident on the image sensor 7 undergoes signal processing in thevideo signal processing circuit 24, and a color signal or a monochromesignal is output as a video signal from the video signal output circuit27.

Next, FIG. 9 showing the variation characteristic in F-number of animage pickup lens, which can have a zoom mechanism with the diaphragmmechanism open, will be described. In general, in an image pickup lens,which can have a zoom mechanism, when the zoom position is changed fromthe wide angle end to the telephoto end, the F-number which indicatesthe brightness of the lens changes according to the zoom position. Whenthe F-number (lens brightness) at the wide angle end is 1.0 and the zoomposition is changed toward the telephoto end, the F-number changes asillustrated in FIG. 9. This characteristic is lens-specific, and lensesof different optical design have different F-number variationcharacteristics. However, lenses of the same optical design havesubstantially the same F-number variation characteristic. The data ofF-number variation characteristic can be obtained in advance in thedesign phase.

In the present exemplary embodiment, the visible light sensor 8 isdisposed at a different position from the image pickup optical system 1.The luminance information of the visible light sensor 8 is compared withthe luminance information of the image sensor 7, which receives lightvia the optical system 1, which can have a zoom mechanism. Therefore, itcan be necessary in some circumstances to consider the zoom position.Let's assume, for example, a case where the zoom position is halfwaybetween the wide angle end and the telephoto end (hereinafter referredto as “middle”). From the F-number characteristic diagram of FIG. 9, theF-number attenuation rate of the optical system 1 is 0.8 times that ofthe wide angle end. That is to say, when the same amount of light isreceived at the lens entrance, the brightness at the middle position isonly 80% of that at the wide angle end. Here, the visible light sensor 8is supposed to show the luminance value of the image sensor 7 providedwith the IR cut filter 4. However, if the photographing mode isdetermined without considering the attenuation of 80% and is switched tothe color photographing mode, the luminance value decreasessignificantly and an image satisfying the intended photographingluminance cannot be obtained or is difficult to obtain. That is to say,if the luminance information obtained from the visible light sensor 8 isnot corrected according to the zoom position, determination is performedon the basis of incorrect luminance information of the visible lightsensor 8. Thus, determination for switching of the photographing modecannot be appropriately performed or is difficult.

Next, the operation of the control circuit 10 in the case where theluminance value of the visible light sensor 8 is corrected or errorreduced according to the zoom position will be described with referenceto the flowchart of FIG. 8. Here, the difference from the firstexemplary embodiment will be mainly described. First, in step S101, thecamera control circuit 21 determines whether or not the presentphotographing mode is the night mode. If the present photographing modeis the night mode, in step S402, the present zoom position of the lensis referred to. Next, in step S403, the luminance value obtained fromthe visible light sensor 8 is corrected or error reduced on the basis ofthe zoom position correction data stored in the zoom position correctiondata storage device 29. The visible light luminance information forexample equivalent to the lens brightness of the image pickup lens 1 atthe present zoom position is then calculated. Thereafter, as in thefirst exemplary embodiment, the luminance information obtained in stepS403 is compared with the luminance information from the image sensor 7,and thereby determination for switching of the photographing mode isperformed.

As described above, in the present exemplary embodiment, the luminanceinformation obtained from the visible light sensor 8 is corrected orerror reduced on the basis of the correction information according tothe zoom position of the image pickup optical system stored in the zoomposition correction data storage device 29. By using the corrected valuefor determining switching of the photographing mode, switching betweenthe color photographing mode and the monochrome photographing mode canbe appropriately performed.

FOURTH EXEMPLARY EMBODIMENT

A fourth exemplary embodiment will be described with reference to FIGS.1, 3, 7, and 10. The configurations of the optical system and thecontrol circuit (FIG. 7) of this exemplary embodiment are the same asthose of the third exemplary embodiment (FIGS. 1 and 7). The softwareoperating the camera control circuit 21 of the control circuit 10 ofthis exemplary embodiment (FIG. 10) is different from that of the thirdexemplary embodiment. FIG. is a flowchart showing the operation of thefourth exemplary embodiment of the present invention. As for FIGS. 1 and3, their descriptions will be omitted because they have already beendescribed. As for the block diagram of the control circuit 10 shown inFIG. 7, its description will be also omitted because it has already beendescribed in the third exemplary embodiment.

Next, the operation of the control circuit 10 will be described withreference to the flowchart of FIG. 10. In the case where the luminancevalue of the visible light sensor 8 is corrected or error reducedaccording to the zoom position, the control circuit 10 checks whether ornot the zoom lens is at rest and then switches between the colorphotographing mode and the monochrome photographing mode. The generalflow of the process of correcting or reducing the error in the luminanceinformation of the visible light sensor 8 with reference to the zoomposition and determining the photographing mode has already beendescribed in the first and third exemplary embodiments. Therefore, onlythe difference will be described.

First, in step S101, the camera control circuit 21 determines whether ornot the present photographing mode is the night mode. If the presentphotographing mode is the night mode, in step S502, it is determinedwhether or not the zoom device is now moving. If the zoom device is atrest, in step S503, the present zoom position of the lens is referredto. Next, in step S403, the luminance value obtained from the visiblelight sensor 8 is corrected or error reduced on the basis of the zoomposition correction data stored in the zoom position correction datastorage device 29. The visible light luminance information equivalent tothe lens brightness of the image pickup lens 1 at the present zoomposition is then calculated. Thereafter, as in the third exemplaryembodiment, the luminance information obtained in step S403 is comparedwith the luminance information from the image sensor 7, and therebydetermination for switching of the photographing mode is performed. Ifthe zoom device of the lens is now moving in step S502, the series ofdeterminations for switching of the photographing mode are not performedand the present photographing mode is maintained.

As described above, in the present exemplary embodiment, the luminanceinformation obtained from the visible light sensor 8 is corrected orerror reduced on the basis of the correction information according tothe zoom position of the image pickup optical system stored in the zoomposition correction data storage device 29. It is determined whether ornot the zoom device is now moving, and only when the zoom device is atrest, determination for switching of the photographing mode isperformed. In this way, the luminance information of the visible lightsensor 8 can be stably corrected even when F-number (lens brightness)varies depending on the zoom position. Therefore, switching between thecolor photographing mode and the monochrome photographing mode can beappropriately performed. Instead of the visible light sensor 8, aninfrared light sensor can be used as the brightness detection device.For example, in the first exemplary embodiment, the luminance value(e.g., brightness information) Ydiff of the infrared component isobtained as the difference between the luminance value (e.g., brightnessinformation) Y1 of the visible light sensor 8 and the luminance value(e.g., brightness information) Y2 of the image sensor 7. In contrast, inthe case where the luminance value (e.g., brightness information) of theinfrared component is obtained using an infrared light sensor, theluminance value Y1 of visible light is obtained as the differencebetween the luminance value Y2 of the image sensor 7 and the luminancevalue of the infrared light sensor. In the above, switching from the daymode to the night mode is performed on the basis of the luminance valueof the image sensor 7, that is to say, the sum of the infrared lightcomponent and the visible light component. Alternatively, the switchingcan be performed on the basis of the luminance value of the visiblelight sensor 8.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

1. An optical apparatus comprising: an image pickup optical systemconfigured to focus incident light beams incident from a subject; animage pickup device for converting a subject image formed by the imagepickup optical system into a first electrical signal; an optical filterconfigured to be inserted into and removed from the image pickup opticalsystem, wherein the optical filter selects a wavelength band of lightbeams incident on the image pickup device; a brightness sensor fordetecting a brightness of the subject and converting the brightness intoa second electrical signal; and a controller for determining whether thefilter is to be inserted or removed, on the basis of at least one of thefirst electrical signal and the second electrical signal, wherein abrightness detection range of the brightness sensor is within animageable range of the image pickup device, and the controllerdetermines whether the filter is to be inserted or removed, on the basisof the second electrical signal and a part of the first electricalsignal corresponding to the detection range of the brightness sensor.